The present invention relates to a friction stir welding method and a structural body which is formed using a friction stir welding method. For example, the present invention is directed to a friction stir welding method and a structural body made of an aluminum alloy extruded as a frame member, such as is used in a railway vehicle or a building structure and the like, formed by friction stir welding.
Friction stir welding is a method in which, by rotating a round rod (called xe2x80x9ca rotary toolxe2x80x9d) which has been inserted into a welding joint between extruded frame members and moving the rotary tool along a welding line of the welding joint, the welding portion is heated, softened and plastically fluidized and is solidly welded. The rotary tool is comprised of a small diameter portion which is inserted into the welding joint and a large diameter portion which is positioned outside of the small diameter portion of the rotary tool. The small diameter portion and the large diameter portion of the rotary tool have the same axis. A boundary between the small diameter portion and the large diameter portion of the rotary tool is inserted to a small extent into the welding joint during welding.
The above-stated technique is disclosed, for example in Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2). In FIG. 9 of this document, it can be seen that a welding of two abutting faces of two hollow extruded frame members is carried out from the opposite side of the hollow extruded frame members. Namely, the plates forming one side face of the two frame members are abutted, and from the other side of the extruded frame members, a friction stir welding is carried out. In this way, the outer face formed by said plates is welded so as to produce a flat surface.
As also shown in FIG. 9 of the above-stated document (Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2)), in a case where a hollow frame member is welded from an opposite side using friction stir welding, it is necessary to strongly fix or secure a joint member 60. For this reason, the joint member 60 is fixed temporarily to the hollow frame members 31 and 32 by arc welding. Since the plate thickness of the joint member 60 is thin, the joint member 60 is subject to strain in a thickness direction by the welding heat. For this reason, there is a problem concerning the accuracy of the form of the structural body resulting from a twisting of the joint member during welding.
An object of the present invention is to provide a friction stir welding method wherein a temporary welding of a connection member to be friction stir welded becomes unnecessary.
The above-stated object can be attained in a case where one face plate of a frame member is welded using a connection member, by using a technique in which a projection at one end of the connection member is inserted into a groove in the frame member so that a proper positioning of connection member is achieved.
The above-stated object can be attained by a friction stir welding method, characterized in that, in preparing a first frame member and a second frame member for welding, wherein the first frame member and the second frame member each have a first face plate and a second face plate disposed in parallel to the first face plate, and the first and second frame members are abutted with the ends of the second face plates in contact with each other and with a third plate for connecting the first face plate and the second face plate, the welding method comprises welding the second face plates together from a side of the first face plates through a gap therein, arranging respective end portions of a connection member between an end portion of the first face plate of the first frame member and the first face plate of the second frame member across said gap by inserting one end of the connection member into a groove which opens toward the second frame member in an end portion of the first face plate of the first frame member, temporarily fixing the other end of the connection member to an end portion of the first face plate of the second frame member, and carrying out a friction stir welding on the end portion of the first face plate of the first frame member and the one end of the connection member followed by friction stir welding of the end portion of the first face plate of the second frame member and the other end of the connection member.
The above-stated object can be attained by a friction stir welded frame member that comprises a first face plate, a second face plate disposed in parallel to the first face plate and a third plate for connecting the first face plate and the second face plate, wherein at an end portion of the first face plate, a groove is provided which opens toward the end portion in a longitudinal direction of the frame member.